Partitioned People Tracking With the Gantry-PTU 5-DOF Robot

By Gary Moore,2014-05-07 13:53
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Partitioned People Tracking With the Gantry-PTU 5-DOF Robot

    People Tracking With the Gantry-PTU 5-DOF Robot


    1. Introduction:

The 5-DOF ceiling-mounted gantry robot can track a person walking around the gantry’s

    workspace, as shown in Figure 1. The demo is a seven-step procedure:

    1. Position the camera using the gantry’s teach pendant 2. Orient the camera with the PTU to point West (see Figure 1 for Cardinal points).

    3. Execute C:\POH\TRACKING\GMOVE2_3.EXE on Robocop 4. Execute ~paul/gantry-demos/Hybrid5_1 on Scallop 5. Enter gains such as 1.0 for the PTU and 2.0 for the gantry

    6. Place SSD over target of interest. Tracking will now follow the person

    7. Pushing the gantry’s pendant red abort button will terminate tracking. Kill the

    Hybrid5_1 Scallop process with CTRL-C and kill the Robocop GMOVE2_3 program

    with ESC and halt the PTU.






    person's trajectory

    Unix machine or X terminalGantry 486 PClogged into scallop(Robocop)

    Figure 1: Top view of gantry workspace. Room's south side points to Uris Hall

2. Details of the Seven Steps

    2.1 Step One: Gantry camera positioning

The gantry is typically always left on and its teach pendant effects gantry motions. Gantry

    positioning places the target in the camera’s general field-of-view. If this is so, then one can

    proceed to Step Two. Occasional power surges or Robocop hard reboots however, can cause

    the gantry to freeze and be unresponsive to teach pendant commands. If this is so, the gantry

    must be rebooted and re-homed.

    2.1.1 Rebooting:

Rebooting the gantry involves first, powering it down then up and second, reloading the

    gantry’s AT6400 operating system. Power down is achieved by switching off the yellow

    power bar. Since, the gantry will immediately translate downwards, it is important to gently

    support the gantry end-effecter while powering down. Switching power on again, one will

    hear the gantry lock into position and one can now freely remove support.

Executing AT6400.EXE on Robocop will load the gantry’s operating system. Once loaded,

    the gantry must be initialized via the FASTTERM.EXE, terminal program:


Accept the 768 default base port address and load the gantry initialization program:

    Hit F1



    Type: psetup

The gantry has been rebooted and initialized. The gantry’s teach pendant will XYZ jogging

    after one types:

    ls 333

    lh 333

    jog 111

2.1.2 Re-homing the Gantry

The gantry’s primary home position is in the North-West corner (see Figure 1). First, bring

    the gantry close to this corner with the teach pendant, then FASTTERM type:


The gantry should begin slowly homing. For people tracking, a secondary home position was

    defined and lies appropriately halfway between the North and South sides of the gantry as

shown in Figure 1. Under FASTTERM, one can load and execute the secondary home


     Hit F1


     Type: homme2

The gantry can be further positioned if desired with the teach pendant. This may be

    necessary to get a good camera field-of-view over the target of interest; one can jog the

    camera vertically, horizontally and set a camera-to-target depth.

    2.2 Step Two: PTU Orientation

The PTU is serially tethered to Scallop via the Central Data Quad-Serial Port Box on port

    /dev/sts/ttyC53 (case sensitive). Via KERMIT, one can execute PTU commands:

    bash$ kermit l \dev\sts\ttyC53

    Type: c

    Type: pp-1750

    Type: tp0

    Type: ee

    Type: ft

    Pan position, pp1750 and tilt position, tp0, orients the camera’s optical axis West as shown in Figure 1. KERMIT must be exited (using the key combination -\ then

    -C) before tracking begins. At anytime, PTU motions can be halted by typing H

    under KERMIT, or by switching off the PTU power supply.

    GMOVE2_3.EXE 2.3 Step 3: Executing

    GMOVE2_3 in C:\POH\TRACKING is a DOS program on Robocop. It executes gantry motion requests issued by Scallop. GMOVE2_3 must be running before Step 4. It’s source code is in the same directory. At essence, GMOVE2_3 receives and transmits ASCII characters, which the AT6400 recognizes as gantry motion commands.

    2.4 Step 4: Executing Hybrid5_1

Hybrid5_1 in ~paul/gantry-demos is a GCC compiled executable and must be run while

    logged into Scallop. Hybrid5_1 begins checking the serial connection between Scallop and

    Robocop (/dev/sts/ttyb) and the serial connection between Scallop and the PTU

    (/dev/sts/ttyC53) and hence KERMIT must not be running simultaneously.

Hybrid5_1 calls X-Vision functions which in turn call X11 routines. The current

    ~paul/.profile LD_LIBRARY_PATH may be incorrect and Hybrid5_1 will complain.

    Unsetting this path will overcome this problem.

2.5 Step 5: Setting Gains

Executing Hybrid5_1 will prompt the user to enter gains. This program suggests a PTU

    gain of 1.0 (a float) and a gantry gain of 2.0 (a float). Larger PTU gains (1.0 < PTU gain <

    2.0) and a gantry gain of 2.0 will track a faster moving person. PTU gains > 2.0 can yield

    unstable results and should be avoided.

    2.6 Step 6: SSD Placement

After gains entry, Hybrid5_1 will display what the camera sees and an 80x80 SSD tracking

    window. Place the SSD window with the mouse, over the person’s head and click.

    Partitioned tracking will begin and the person can freely walk around the gantry workspace.

The camera view and SSD window are displayed on the black and white video monitor. If

    the SSD loses the target, it is important to quickly kill the gantry (teach pendant abort push

    button), kill the Hybrid5_1 process, kill GMOVE2_3 and halt the PTU. This same procedure is used to terminate the demo and is explained in the following steps.

    2.7 Step 7: Terminating the Demo

Pushing the red button on the gantry teach pendant at anytime, will abort all gantry motions.

    This push button is the one located closest to the pendant’s tether cable (see Figure 2)




    Figure 2: Gantry teach pendant

    Pushing the abort button however will not terminate the Hybrid5_1 process, nor the GMOVE2_3 program. A simple CTRL-C will kill Scallop’s Hybrid5_1 process and hitting ESC on Robocop will kill GMOVE2_3. The PTU should also be halted since it is possible that the PTU is still panning and/or tilting because it is executing the last command

    before Hybrid5_1 was terminated. Under KERMIT, via -l /dev/sts/ttyC53, one types H

    and to immediately halt all PTU motions.

    3. Appendix

This robot is a hybrid consisting of a variety of components, see Figure 3, which work

    together to track a moving target. Tracking will failure if any component is not properly

    configured or properly wired. This Appendix gives some common trouble-shooting tips and

    wiring diagrams and concludes with other directories of interest in ~paul. This can be of help to future developers.

    Figure 3: 5-DOF hybrid robot

     The components are:

    ? Gantry robot and its 486 PC (named Robocop)

    ? Pan-tilt-unit (PTU) serially connect to Scallop off /dev/sts/ttyb

    ? K2T framegrabber installed in Scallop

    ? Scallop-Robocop serial connection off /dev/sts/ttyC53 3.1 The black and white monitor is not displaying what the camera sees

    Scallop Sparc 20(viewed from rear)

    Y: yellowK2T LEFTK2T OUTR: redBBGGG: greenRYYRB: blue




    Figure 4: Camera, K2T framegrabber, PS-12 SU sync box and monitor cabling

    Figure 4 illustrates the camera/K2T/sync-box/monitor wiring. The monitor should display

    what the camera sees if one uses the cabling in Figure 4. Refreshing the K2T framegrabber

    can also help using the go_live program:


    Note the colored cables and their connections depicted in Figure 4. Hybrid5_1 is hard-coded to use camera images through the K2T green channel.

    3.2 Hybrid5_1 complains about serial connections

There are two serial connections in the setup. The first is the serial connection from

    Scallop’s /dev/sts/ttyb serial port to Robocop’s COM1 serial port. If serial cable between these two computers is not connected, Hybrid5_1 will complain and state a failure to

    establish gantry communications. It is thus important to check that this serial cable is

    properly connected.

    The second serial connection is between Scallop’s /dev/sts/ttyC53 and the PTU. The Central Data quad serial port box provides the ttyC53 serial port. Hybrid5_1 is hard-coded to work with /dev/sts/ttyC53 (case-sensitive). Hybrid5_1 will complain of a failure to establish PTU communications if this port is not working. If one can use KERMIT to issue

    PTU ASCII commands with this port, then Hybrid5_1 should also work with this port. Again, it is important to make sure this serial cable is properly connected. For reference,

    Figure 5 is the serial cable pin out between Scallop and the PTU.









    Figure 5: PTU-to-Scallop serial cable pin out

    3.3 KERMIT works with the PTU, but Hybrid5_1 still complains

Hybrid5_1 is hard-coded to work with the PTU under terse feedback terse (ft) and echo

    enabled (ee). Section 2.2 gave details on setting this PTU configuration:

    bash$ kermit l \dev\sts\ttyC53

    Type: c

    Type: pp-1750

    Type: tp0

    Type: ee

    Type: ft

Hybrid5_1 reads strings generated by the PTU. Terse feedback returns shorter ASCII

    strings than under verbose feedback. Return strings commence with an asterisk which is

    Hybrid5_1 uses. Some other executables in ~paul/Gantry-partitioning turn echoing off to decrease program cycle time (thus increasing bandwidth), but Hybrid5_1 in the demo uses echoing.

    3.4 pp-1750 doesn’t orient the PTU west

pp0 points the camera south (towards Uris Hall) and is the PTU’s default home orientation.

    Issuing -1750 steps clockwise (as viewed from above) via a pp-1750 command should point the camera west. The PTU resolution is 0.0514 degrees/step, thus 0.0514 * 1750 steps ~ 90


If pp0 doesn’t point the camera south, then possible the PTU was mounted on the gantry end

    effecter in the reverse orientation. The camera would then be pointing north. Because

    Hybrid5_1 couples the PTU orientation to the gantry’s X-axis (Motor 1), the PTU should be re-mounted to point the camera south when at pp0.

By default, the PTU is configured with limits enabled (ASCII command le). If not enabled,

    a pan orientation beyond ?3000 steps or a tilt orientation beyond ?600 steps could mechanically force the PTU past its Hall effect limit switches. When this occurs, the PTU

    will no longer be calibrated properly; issuing pp0 will fail to servo the PTU to a right-angle

    orientation. Under these circumstances, the PTU typically grinds (having hit its hard limit)

    after issuing a reset command (ASCII command r). To overcome this, one has to open up and manually turn the PTU into its default PTU orientation. The PTU housing can be

    opened with an Allen key, and oriented by turning the gears by hand. A r command should then reset the PTU properly.

    3.5 Other source code and executables in ~paul

Directories of interest to developers under ~paul are:

gantry-serial: examples in Scallop-to-Robocop serial communications

    gantry-demos: various demos

    gantry-partition: partitioned control development

    gantry-depth: recursive least squares camera-to-target depth development

gantry-programs: array handling functions

    gantry-test: AT6400 .prg code - loaded and executed under Robocop

    gantry-dperception: Directed Perceptions PTU binaries (compiled by Atanas)

    gantry-time: Unix gettimeofday() examples for timing program cycle time

    gantry-figures: figures used in ICRA publications and thesis

    gantry-ptu: programs to servo the PTU with serial ASCII commands

    gantry-tracking: 3 DOF pose regulation (block tracking with 4 fiducials)

    gantry-ptu-tracking: 5 DOF pose regulation development

    gantry-vision: K2T code, old and new versions of X-Vision

    gantry-kalman: examples of Kalman filter for estimating camera-to-target depth

    gantry-rccl: Vicky Puma 560 servo programs using RCCL libraries

Gantry-binarized: partitioning using Directed Perceptions’ PTU binaries

    Gantry-sin: various programs used for Bode system ID of gantry and PTU

    Gantry-time: programs used to measure program cycle time

    Gantry-depth: recursive least squares for measuring camera-to-target depth

    Gantry-partition: people tracking, corner handling, depth handling development

    Each directory has a 00index text file which describes directory contents. There is a distinction between directory names with the leading gantry- and Gantry- prefix. The former

    are programs compiled with the an older version (prior to January 1999) of X-Vision. The

    latter are programs compiled with the newest version of X-Vision (as of July 2000). This X-

    Vision release has additional features like SSD scale factors (used in depth regulation

    programs) and frame-acquisition timing. I used the convention of leading a filename with an

    uppercase if it was compiled using the newer X-Vision version (e.g. Hybrid5_1).

    Lowercase was used if compiled in the older version (e.g. hybrid5_1).

Robocop also has useful code under the C:\POH directory.

TRACKING: GMOVE development (compiled under Borland C DOS version)

    SETUP: AT6400 gantry initialization setup programs

    MYPROGS: AT6400 programs (*.prg) written for commanding gantry motions

Paul Oh

July 2000

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